It is necessary to obtain a fracture characteristic value of a pipe structure in order to apply leak before break (LBB) analysis results to the pipe structure so as to prevent problems, such as an accident occurring at a nuclear power plant. However, a great number of pipes and test devices are used to obtain the fracture characteristic value of the pipe structure, which is costly and takes much time, making it very difficult to conduct a proof test.
Therefore, rather than using a large number of pipes and test devices, a method of obtaining a fracture characteristic value of a material through a standard specimen test, analyzing the pipe structure based on the fracture characteristic value, and evaluating the fracture characteristics has been suggested.
The Standard Test Method for Measurement of Fracture Toughness (ASTM E1820) provides the size and shape of a compact tension (CT) specimen or a single edge notched bending (SENB) specimen that are standard specimens suggested by the American Society for Testing and Materials (ASTM). In more detail, referring to FIG. 7, a CT specimen 600 is in a rectangular planar shape. A mechanically processed notch portion 612 is formed in one side of the CT specimen 600. A crack portion 614 is formed at the edge of the notch portion 612. Two openings 618 and 619 are formed in the upper and lower portions of the CT specimen 600. The notch portion 612 is disposed between the openings 618 and 619. A bending load is applied to the openings 618 and 619 by using a pressurizing unit such as a pin, thereby obtaining the fracture characteristic value of the material.
Referring to FIG. 8, an SENB specimen 700, which has a mechanically processed notch portion 712 and a crack portion 714 formed at the edge of the notch portion 712 is applied. A bending load is applied to the SENB specimen 700, and the fracture value of the material is obtained.
As described above, although there is an advantage in that the conventional standard specimen has a standard specimen shape and testing method, specimen manufacture is restricted in terms of the curvature and thickness of a pipe.
Furthermore, the fracture characteristic value should be obtained in consideration of a constraint effect of a geometrical shape or size of the specimen, and the pipe structure is greatly influenced by the constraint effect. Therefore, although the standard specimen is used to conduct a test, it is necessary to compensate for the influence of the constraint effect due to varying sizes and shapes of pipes to be actually used.
Moreover, it is difficult to process the conventional CT specimen shown in FIG. 7 due to the complicated shape thereof, and the conventional SENB specimen shown in FIG. 8 consumes a great amount of materials despite being easily processed.